This invention relates to a method of converting a fluorine-containing high polymer such as, for example, polytetrafluoroethylene into a wax-like lower molecular weight polymer.
Relatively low molecular weight polymers and copolymers of some fluorine-containing organic compounds are known for their excellent lubricating property and characteristically low surface energy and accordingly are widely used as lubricants, releasing agents, etc. Particularly, low molecular weight polytetrafluoroethylene (PTFE) is popular by the common name of tetrafluoroethylene (TFE) wax.
A well known and industrially employed method for preparing TFE wax is telomerization of TFE. However, this method has many problems difficult to solve satisfactorily. For example, where a compound employed as the telogen is utilized also as reaction medium, very complex techniques are required for controlling the reaction conditions and also for controlling the molecular weight of the product. Besides, separation of the monomer and the telogen from the telomer is not easy. Where an aqueous reaction medium is used, major problems reside in insufficiency of thermal stability of the synthesized wax and difficulty in separating unreacted monomer from the telomer.
Another way to obtain TFE wax is to reduce the molecular weight of PTFE by controlled thermal decomposition. According to proposals already made for this purpose, PTFE is thermally decomposed to a desired extent in the presence of a catalytic substance such as silicon, aluminum, magnesium or graphite, or in the presence of a sort of degradation promoter such as air, oxygen, sulfur dioxide or nitric monoxide, or in a fused salt such as potassium or sodium nitrate. A problem inherent to such thermal decomposition methods is the generation of noxious gases of which disposal is very troublesome in industrial practice. There is another problem that the quality of the product is unintendedly variable when scrap of PTFE is used as the raw material by reason of expensiveness of PTFE.
Recently, controlled decomposition of PTFE by radiation such as X-ray or gamma-ray is under development. From an industrial point of view, however, using radiation is generally unwelcome because it is troublesome and usually costly and requires regulation facilities.